Any reason you can't use Apple's free Pages or any of the billion other text editing programs?
For me, the incomparable advantage of TextEdit is that it understands Apple's Desktop Workspaces.
I currently have 21 Desktop workspaces and most of them have open TextEdit window where I record project notes and To Do lists. I can reboot my computer and all of my TextEdit windows (including ones that were in Edited mode and not saved!) will be on the desktops where I originally had them. Most other word processors will not automatically reopen whatever windows had been there, and if they do, all of the windows will be in the first desktop, leaving me the onerous task of moving everything to where it had been before, out of a mountain of windows on that first desktop. Even Stickies does that, contradicting its name.
I wish I could change the default margins, but being able to change them straightforwardly, under the hood in the RTF, and use that as a template works well enough. I wish TE had a Markdown mode and a collapsing outliner mode and ... a whole bunch of things, including VIM's keyboard commands for editing.
No, it's not a replacement for Pages or Word. This discussion of margins is typical. It's use of Styles, if you can find it under Fonts and can understand it's kludgy UI, is limited but still useful. And it's not a replacement for VIM or Emacs or any code editor that is smart about the language you are coding in so that it can do syntax highlighting and code collapsing.
What makes TE essential for me is that I can use it as an ongoing, working notes tool, because I can pretty much count on things not getting lost. The computer can crash and when I reboot, even my unsaved notes are still there, on the right desktop, in the right location on the screen. No other text editor or word processor can touch that.